Who does contribute to Wikipedia?
Gender
84 / 100
The 2013 study The Wikipedia Gender Gap Revisited measured gender bias in survey completion and estimated that as of 2008, 84% of English Wikipedia editors were male. In the worldwide Wikipedia Editor Survey 2011 of all the Wikipedias, 91% of respondents were male.
Nationality
The greatest number, or plurality, of editors (20%) reside in the United States, followed by Germany (12%) and Russia (7%). The only country not in Europe or North America in the top 10, is India (3%).
Age distribution
13 / 100
13% of editors are under 17.
14 / 100
14% are in the group 18–21.
26 / 100
26% are 22–29.
19 / 100
19% are 30–39.
28 / 100
28% editors are aged 40+.
59 / 100
59% of the editors are aged 17 to 40.
Further information: Wikipedia community and Wikipedia:Wikipedians
The English Wikipedia currently has 32,949,934 users who have registered a username. An unknown but relatively large number of unregistered Wikipedians also contribute to the site. About 250,000 new accounts are created every month. About 300,000 editors have edited Wikipedia more than 10 times. 138,096 have performed an edit within the last 30 days.
The type of people who were drawn to writing an encyclopedia for fun tend to be pretty smart people.
— Jimmy Wales · Founder of Wikipedia, July 2005 -TEDGlobal conference
Contributions come from diverse demographic and ethnographic segments:
mid-20s males and retired males - are the largest demographics
10% - 20% women of various ages - significant underrepresentation acknowledged by Gender bias on Wikipedia and Gender gap
students (e.g., in the context of a course)
enthusiasts (e.g., people with interest in a particular subject, like butterflies)
insiders (e.g., people who work for an organization, such as the Sierra Club)
dabblers (e.g., people who see some problem with an article and want to help)
scholars (e.g., researchers who want to use Wikipedia as an additional dissemination platform)
archives (e.g., a museum, archive or library wanting to contribute artifacts, like 18th-century paintings)
marketers (e.g., individuals, staff, members, or a PR firm seeking to promote a product, service or brand)
evildoers (e.g., spammers, vandals).
Many people in the Wikipedia community are conscious that the demographics of who edits the site can lead to systemic bias in the content of the site and there are efforts to remedy these biases.

How do editors contribute to Wikipedia?
Main page: Wikipedia:Contributing to Wikipedia
The content of any particular article is subject to editorial discretion developed via consensus. Wikipedia is not paper, which means we can write almost an unlimited amount on any topic. Still, there are limits on what we ought to include, and especially how we ought to write it. When an article is incomplete or inaccurate, you can edit the article to be more accurate and/or useful. Someone may place a notice at the top of the article indicating that it needs to be cleaned up. It is also possible to create a new article to share information that is not yet in Wikipedia.
The way to decide whether a particular statement is accurate is to find independent reliable sources to affirm that statement, such as books, magazine articles, television news stories, trade journals, or other websites. For more guidance on evaluating the accuracy of Wikipedia articles, see researching with Wikipedia. It is Wikipedia's policy to add to the encyclopedia only statements that are verifiable, and not to add original research. The Wikipedia style guide encourages editors to cite sources. Detailed citations allow readers of the article to easily verify the content in question.
When a large group of people work to compile information on a given topic, disputes may arise. A useful feature of Wikipedia is the ability to tag an article, or a section of the article, as subject of a dispute about a neutral point of view. This feature is especially popular for controversial topics, topics subject to changing current events or other topics where divergent opinions exist. To resolve the dispute, the interested editors will share their points of view on the article's talk page. They will attempt to reach consensus so that all valid perspectives can be fairly represented. This allows Wikipedia to be a place not only of information, but of collaboration. Many users of Wikipedia consult the page history of an article in order to assess the number, and the perspective, of people who contributed to the article. You may also consult the talk page of any article to see what other readers and editors have to say about it.
Wikipedia's best articles are highlighted in the list of featured articles. These articles were granted "featured" status because they were judged to be of high quality by other editors and users. (If later edits reduce the quality of a featured article, a user can nominate an article for removal from the list.)